This invention relates to an instrument and method for measuring tack and more particularly to a portable tack tester.
There is a widespread need for a more efficient and reliable measurement of the physical property of tack of elastomeric materials including rubber materials. Tack is defined as the ability of two uncured rubber or elastomeric surfaces to adhere together upon contact under moderate pressure. Tack has also been defined as the force per unit area required to separate two like pieces of rubber or elastomeric material after pressing them together. This is often called autohesion. Tack is to be distinguished from stickiness which is the force per unit width required to separate a piece of rubber or elastomeric compound from some other material, usually steel. Most of the present instruments commercially available measure tack by determining the pull required to separate one sample surface from another by the force exerted in a direction that is perpendicular to the surfaces of the sample. Another instrument measures the peeling forces where one sample of rubber material is peeled away from a second sample in a direction parallel to the adhered surfaces with the result expressed as force per unit width of the strip. Both of these instruments and their corresponding methods measure the maximum force per unit area or per unit width. In preparing samples for testing in these above instruments, it is required that samples or specimens be cut by a die cutting machine to assure the operator that the edges of the sample to be tested be perpendicular to each other. The present invention is directed to a portable tack tester that eliminates the need for precise cutting out of samples wherein the tack tester can measure tack directly at a work station or taken to the processing line as on a tread tuber line. This invention includes a new and novel mechanism for securing the sample. A unique feature of the invention is that in its measurement of tack, the instrument takes into account the time value to thereby express the tack measurement in terms of energy. In contrast to force per unit area the applicant's units of measurement are in terms of energy per unit contact area. The significance of this method is that there is a strong correlation between the tack measurement and the factory experience for quality control of factory production in a factory environment.